Process for melt spinning linear polyester modified with an oxysilicon compound



3,335,211 PROCESS FOR MELT SPINNING LINEAR POLY- ESTER MODIFIED WITH AN OXYSILICON COMPOUND Edward J. Mead, Wilmington, Del., and Cecil E. Reese, Kinston, N.C., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Mar. 7, 1967, Ser. No. 621,147 3 Claims. (Cl. 264-176) ABSTRACT OF THE DISCLOSURE A process is disclosed for preparing and melt spinning glycol terephthalate polyester into textile fibers which provide fabrics having improved resistance to pilling. Anhydrous polyester modified with an oxysilicon compound is prepared to have a melt viscosity at 275 C. of about 1000 to 6000 poises, is melt spun to form fibers, and the fibers are exposed to moisture. Fibers are readily prepared in this way which have a relative viscosity of 10 to 17 needed to improve the pill resistance of fabrics. This is in contrast to unmodified polyester of the same relative viscosity which has such a low melt viscosity during melt spinning, in the range of only 500- to 1000 poises, that it is quite difiicult to maintain satisfactory product uniformity and freedom from filament discontinuities.

Cross-references to related applications This is a continuation-in-part of our copending application Serial No. 450,197 which was filed Apr. 22, 1965, as a continuation-in-part of application Ser. No. 130,764 (now abandoned) filed Aug. 11, 1961, as a continuationin-part of our application Ser. No. 815,808, filed May 26, 1959 (now abandoned).

Specification This invention relates to a process for producing fibers of glycol terephthalate polyesters and is more particularly concerned with an improved process in which the meltviscosity of glycol terephthalate polyester is enhanced for effective spinning into low molecular weight polyester textile fibers, especially pill-resistant staple fibers.

Polyethylene terephthalate, the preparation of which is described by Whinfield and Dickson in their US. Patent No. 2,465,319, dated Mar. 22, 1949, has attracted high commercial interest for many uses owing to its high tenacity, flexibility, crease resistance, low moisture absorption, and other valuable properties. Fabrics prepared from fibers of polyethylene terephthalate have become well known for their ease-of-care properties associated with fast drying, crease recovery, and wrinkle resistance as well as for their strength and abrasion resistance.

However, the use of polyethylene terephthalate staple fibers for certain end uses has been greatly restricted by a phenomenon known as pilling, which refers to the accumulation on the surface of a fabric of numerous unsightly small balls of fiber, sometimes with the inclusion of foreign materials. Although attempts have been made to eliminate the phenomenon of pilling by .Various fabric treatments, such attempts have met with only limited success. Solutions which have been suggested include, for example, special fabric treatment combinations of brushing, shearing, and singeing to remove loose fiber ends from the fabric surface.

Many attempts have also been made to modify the polyethylene terephthalate fiber itself in order to inhibit the tendency towards pilling in staple fabrics. It was early recognized that the unsightly effect of pilling was States Patent not due so much to the formation of pills, which occurs in all fabrics prepared from staple fibers, but to the difficulty in wearing off the pills once formed, since the high strength and abrasion resistance of polyethylene terephthalate prevents their rapid removal during normal use of the fabrics.

One of the best solutions of the problem found up to the present time has been to prepare the fibers from polymer of relatively low molecular weight, characterized by sharply-reduced viscosity values, as more fully defined below. In general, fibers of polyethylene terephthalate and its copolyesters exhibit little or no pilling when prepared from polymers having a relative viscosity ofabout 12, while at a relative viscosity of about 20 the pilling problem is already quite severe. A practical lower limit on the relative viscosity of the polymer is imposed by the need for adequate yarn physical properties such as abrasion resistance, which is poor at low relative viscosities, especially below 10. In the case of polyethylene terephthalate homopolymer, a relative viscosity range of about 13 or 14 to about 17 appears to be optimum for providing fibers having good physical properties while at the time exhibiting relative freedom from pilling. The same limits, or slightly different limits in the same general range, apply for the various synthetic copolyesters comprised predominately of ethylene terephthalate structural units.

In contrast to the low level of polymer relative viscosity which has been found desirable for producing yarn exhibiting freedom from pilling, the usual commercial practice has been to spin polyethylene terephthalate and its copolyesters at relative viscosities in the range of 25 to 30. Unfortunately, in attempting to reduce the relative viscosity of the spun polyethylene terephthalate, it has been found that the difliculty in spinning the polymer rapidly increases as the relative viscosity is reduced below the level of about 20. This is apparently due to the lowering of the melt viscosity of the polymer as the level of relative viscosity is reduced. Since the lowest practical melt-spinning temperature is about 275 C., that temperature is used herein for determining melt viscosity. Melt spinning of satisfactory products is quite diflicult when the polyester has a melt viscosity below 1000 poises. The chief problems encountered when the melt viscosity is low are maintenance of the uniformity of product and continuity of spinning of the molten filaments without the formation of drips. Thus, the problem is to extrude glycol terephthalate polyester fibers at the highest practicable melt viscosity within the range of about 1000 to 6000 poises and yet produce fibers of polymer having a relative viscosity of approximately 10 to 17, although such polymer normally has a melt viscosity in the range of only about 500 to 1000 poises.

It is an object of this invention to provide a process for producing and melt-spinning a novel glycol terephthalate polyester composition which exhibits high melt viscosity during spinning but low relative viscosity after spinning. Another object is to provide such process for producing highly-uniform glycol terephthalate polyester fibers, particularly polyethylene terephthalate fibers, from which may be prepared fabrics which are substantially free from pilling. These and other objects will be apparent from the following description and claims.

The present invention is an improvement in the process of melt spinning a glycol terephthalate polyester to produce textile fibers of sufficiently low molecular weight to substantially decrease pilling in fabrics containing the fibers, which conventionally includes melt-polymerization of an ester of terephthalic acid and a glycol of 2 to 18 carbon atoms free from aliphatic unsaturation, in the presence of a condensation catalyst, to a final temperature of about 250 to about 300 C. and a final pressure of less than 10 mm. of mercury to form an anhydrous melt. The improvement of this invention comprises conducting said melt-polymerization in the presence of a condensation catalyst selected from the group consisting of glycol-soluble compounds of antimony or titanium and adding an oxysilicon compound prior to melt spinning to form an anhydrous melt having a melt viscosity at 275 C. of about 1000 to about 6000 poises, said oxysilicon compound being added in the proportion of about 0.1 to 0.75 gram atom of silicon in the added compound per 100 gram mols of said glycol component in the polyester and being selected from the group consisting of wherein R, R and R" are selected from the group consisting of hydrocarbyl and oxyhydrocarbyl radicals of 1 to 6 carbon atoms, Z is a divalent saturated hydrocarbon group of 1 to 6 carbon atoms, x is a number from 1 to 20, and n is a number from to 2; maintaining said polyester anhydrous and melt-spinning it to form fibers; and finally exposing the spun fibers to moisture.

Preferably, the fibers are melt-spun from an oxysiliconmodified polyester anhydrous melt having a melt viscosity at 275 C. of at least 1500 poises.

After the fibers of oxysilicon-modified polyesters have been exposed to moisture, the fibers so prepared are characterized by sharply reduced molecular Weights, as measured by viscosity determinations carried out on the fibers, particularly when compared with corresponding polyester fibers of glycol terephthalate structural units containing no silicon but spun at the same melt viscosity.

By spinning at melt viscosity levels of 1000 to 6000 poises (preferably 1500 to 6000 poises) in accordance with the invention, uniformity of spinning is greatly facilitated as contrasted to spinning at lower levels of melt viscosity. The fibers so produced are uniform and of high quality. However, it has been found that the fibers are composed of much lower molecular weight polyester than would be expected from the viscosity of the anhydrous melt, and exhibit much greater freedom from pilling in fabric form than fibers of polyesters containing no silicon and spun at the same melt viscosity. Apparently exposure to moisture, even the normal exposure of fibers to atmospheric humidity which occurs in fiber-manufacturing operations, causes hydrolysis of oxysilicon linkages in the structural chain of the polyester with resultant reduction of the molecular weight of oxysilicon-modified polyester fibers.

As discussed below, the anhydrous polyester melt is formed by melt polymerization of a glycol terephthalate in the presence of a condensation catalyst which is a glycol-soluble compound of antimony or titanium and preferably in the presence of a silicate ester such as tetra ethyl silicate or other hydrocarbyloxysilicon compound, or an oxyhydrocarbyloxysilicon compound, containing at least two groups capable of undergoing polycondensation with glycol terephthalates, including at least one oxygen atom directly linked to both a silicon atom and a carbon atom. Surprisingly, the hydrocarbyloxysilicon or oxyhydrocarbyloxysilicon compound may be added even after the polymerization step has been completed.

At the conclusion of polymerization the polyester is in the form of an anhydrous melt. It is essential to maintain the polyester anhydrous prior to spinning'This is normally done by keeping the polyester molten prior to spinning; or, if it is desired to solidify and remelt the polyester, extreme care is used to maintain the polyester anhydrous by exclusion of all moisture, even moist air. After the fibers are formed, they are exposed to moisture. This is accomplished by contacting the fibers with an aqueous textile finish or other aqueous processing liquid, or simply by exposing the fibers to moist air for a day or so. The fibers so prepared are characterized by sharply I tached only to oxygen and each silicon is separated by no a .4 reduced viscosity values, as compared with a conventional glycol terephthalate polyester fibers spun at the same melt viscosity.

The amount of silicon-containing additive employed should be such that about 0.1 to 0.75 gra-m atom of silicon is added per gram mols of the glycol component in the glycol terephthalate polyester. Since an excess of glycol is normally employed in the polymerization, it is important to note that the amount of silicon compound added is calculated on the basis of the amount of glycol component present at the conclusion of the polymerization reaction. Preferably, at least about 0.25 gram atom of silicon per 100 gram mols of the glycol component is used.

Examples of suitable hydrocarbyloxysilicon compounds having the formula R[OSi(OR) OR which may be employedin accordance with this aspect of the invention, include the silicate ortho esters wherein x is 1. In such esters R is a radical such as methyl, ethyl, 2-hydroxyethyl, butyl, phenyl, anthryl, naphthyl, or p-tolyl or similar alkyl, aryl, or mixed groups. These esters are commonly identified as tetramethyl orthosilicate, tetraethyl orthosilicate, tetra(2 -hydroxyet-hyl)orthosilicate, etc. Mixed esters may also be employed. Silicate esters may be formed in :situ, such as by adding a silicon halide to an alcohol or glycol and heating the mixture. Disiloxanes such as hexaethoxydisiloxane and polysiloxanes such as ethyl polysilicate are additional examples of soluble silicate esters. In the disiloxanes x is 2, while for polysiloxanes x in the above formula may be any number up to about 20. In all of these compounds silicon is atmore than one atom from a carbon atom, there being at least four oxygen atoms in each compound which are directly linked to both a silicon atom and a carbon atom of a hydrocarbyl or oxyhydrocarbyl radical.

When any of the above silicate esters is added to the polymerization mixture, ester interchange reactions occur with the glycol or terephthalate ester thereof in which the hydrocarbyl or oxyhydrocarbyl radicals of the silicate additive are replaced by the hydrocarbyl residues of the glycol. A recurring mid-chain hydrocarbyloxysilicon structural unit is thereby produced, comprised of carbon, hydrogen, oxygen, and silicon, which forms an integral part of the main polymer chain of recurring glycol terephthalate radicals, the. attachment proceeding through oxygen directly attached both to silicon and to the terminal carbon atom of a glycol residue. Glycol terephthalate side chains may also be formed, and some degree of cross-linking is not excluded, although in the melt viscosity range of 1000 to 6000 poises the composition remains melt-'spinnable; and the polyester in fiber form after hydrolysis of the silicon-to-oxygen linkages is linear. The amount of silicate additive employed is such that at least about 0.1 gram atom of silicon, and preferably at least 0.25 gram atom of silicon, is added per 100 gram mols of the glycol component in the glycol terephthalate polyester. However, amounts of silicate additive greater than about 0.75 gram atom of silicon per 100 gram mols of the glycol component are usually not employed owing to the very low relative viscosities of the spun filaments which are thereby achieved.

Other suitable hydrocarbyloxysilicon compounds which may be employed in accordance with this aspect of the invention include organosilicon compounds of the formulas:

as defined above. In these compounds there is at least one oxyqgen atom directly linked to both a silicon atom and a carbon atom of a hydrocarbyl or oxyhydrocarbyl radical and, when there is only one such oxygen atom, the compound also contains a carboxyhydrocarbyl radical joined to the silicon atom by a direct carbon-to-silicon bond. Examples of the above compounds include fi-carbethoxyethyltriethoxysilane, ,B-carbethoxypropyltriethoxysilane, ,B-carbethoxypropylmethyldiethoxysilane, methyltriethoxysilane, diethyldiethoxysilane, ,B-hydroxyethyltriethoxysilane, diphenyldiethoxysilane, dimethyldibutoxysilane, phenyltriethoxysilane, fi-carbethoxyethyldimethylethoxysilane, di(B-carbethoxyethyl)methylethoxysilane, and diphenyldiphenoxysilane.

When any of the above organosilicon compounds is added to the polymerization mixture, esterification or ester interchange reactions occur with the glycol or terephthalate ester thereof and a recurring mid-chain hydrocarbyloxy silicon structural unit is produced, comprised of carbon, hydrogen, oxygen, and silicon and forming an integral part of the main polymer chain of recurring glycol terephthalate radicals, the attachment proceeding through oxygen directly attached both to silicon and to the terminal carbon atom of a glycol residue. Glycol terephthalate side chains may also be formed, and some degree of cross-linking is not excluded, although in the melt viscosity range of 1000 to 6000 poises the composition remains melt-spinnable; and the polyester in fiber form after hydrolysis of the silicon-to-oxygen linkages is linear. As in the case of the silicate esters, the amounts of organosilicon compound added is in the range of about 0.1 to about 0.75, preferably 0.25 to about 0.75, gram atom of silicon in the added compound per 100 gram mols of the glycol component of the glycol terephthalate polyester.

In one embodiment of the invention, an ester of terephthalic acid and a glycol is melt polymerized to form a polyester composed essentially of glycol terephthalate recurring structural units as a starting material free of silicon-containing additive. It has been found that when the starting material polyester is treated With a hydrocarbyloxysilicon compound of one of the formulas shown above, the product which is formed has a melt viscosity equal to or greater than that of the starting material polyester but a lower relative viscosity than the starting material polyester. An amount of hydrocarbyloxysilicon compound is added to provide in the range of about 0.1 to about 0.75, preferably 0.25 to about 0.75, gram atom of silicon in the added compound per 100 gram mols of the glycol component of the glycol terephthalate polyester. Surprisingly, a uniform product which is readily meltspun is rapidly formed in the melt. After the product is formed, it must be maintained anhydrous prior to meltspinning, since contact of the product with Water or water vapor will reduce the melt viscosity of the pol ester to the normal level associated with the final relative viscosity.

In a preferred embodiment of the invention, an ester of terephthalic acid and a glycol is melt polymerized in the presence of a hydrocarbyloxysilicon compound of one of the formulas shown above and in the amounts specified. This embodiment is particularly preferred since the polymerization reaction itself provides for thorough mixing of the additive and because the additive is com pletely soluble in the mixture, at least by the conclusion of the polymerization. Uniformity of product is thus readily achieved.

The present invention provides a controlled method for enhancing the melt viscosity of polyesters Within a range of from several percent to several hundred percent, as desired, to produce polyester fibers of a given level of relative viscosity. The difierential in melt viscosity, at

equal levels of relative viscosity of the filaments of modified or unmodified terephthalate polyesters, increases with increasing silicon content and, in cases wherein colloidal forms are incorporated in the polymer, with decreasing particle size.

If the modified polyester is prepared in an autoclave and the molten polyester is quenched with water in the usual manner prior to flake preparation, the polyester will not possess enhanced melt viscosity with relation to its relative viscosity when it is remelted for spinning. In fact, an enhanced melt viscosity will not even be observed if the polymer is merely exposed to the water vapor existing in ordinary room air. Drying the polyester by normal methods, once it has been exposed to Water, does not restore the enhanced melt viscosity. Surprisingly, however, if the modified polyester is maintained under dry conditions in accordance with the invention, the enhanced melt viscosity can be utilized to its full elfect in the spinning operation. A convenient method for maintaining the modified polyester dry prior to spinning is to maintain it in the molten condition between the addition of the silicon-containing material and its extrusion into filaments. Subsequent to the extrusion of the filaments from the spinneret the filaments are processed in the normal manner without maintenance of anhydrous conditions.

Formulas and definitions As used herein, hydrocarbyl radicals refer to radicals derived from hydrocarbons. While there is no critical upper limit to the size of the hydrocarbyl radicals in the oxysilicon compounds designated above, the hydrocarbyl radicals generally do not contain more than about 6 carbon atoms and are free of aliphatic unsaturation. The hydrocarbyl radicals thus comprehend both alkyl (including cycloalkyl) and aryl (including aralkyl) radicals containing up to about 20 carbon atoms. The hydrocarbyl radicals may carry substituents inert in the polycondensation reaction; for example, an aromatic radical may carry a halogen, acetyl, or arylsulfonyl substituent. Similarly, oxyhydrocarbyl radicals are hydrocarbyl radicals containing an oxygen atom which forms a direct linkage between two carbon atoms or is bonded to carbon and hydrogen, hence includes ether and/ or hydroxy groups. Carboxyhydrocarbyl and hydroxyhydrocarbyl radicals are correspondingly hydrocarbyl radicals containing carboxy or hydroxy groups which may also contain other oxy groups.

Silicate esters of the formula where R and x are as defined above, may alternatively be designated as hydrocarbyl and oxyhydrocarbyl silicates. Used in this sense, the term silicates is intended to comprehend polysilicates. It should be noted that when the silicate esters are added to a reaction mixture containing an excess of the glycol, G(OH) ester interchange between the glycol and silicate ester takes place with replacement of the radical, R, by the radical, HOG; so that, in many instances, the effective reagent in the polycondensation reaction is actually the glycol ester of the silicate.

Similarly, alternative designations for the other organosilicon compounds previously disclosed, comprehend the hydrocarbylsilicon tri(hydrocarbyloxides) and tri(oxyhydrocarbyloxides),

the di(hydrocarbyl)silicon di(hydrocarbyloxides) and di (oxyhydrocarbyloxides),

the hydrocarbylhydroxyhydrocarbylsilicon hydrocarbyloxides and oxyhydrocarbyloxides as well as the hydrocarbylcarboxvhvdrocarbylsilicon hydrocarbyloxides and oxyhydrocarbyloxides, e.g.,

and the hydroxyhydrocarbylsilicon hydrocarbyloxides and oxyhydrocarbyloxides as well as the carboxyhydrocarbylsilicon hydrocarbyloxides and oxyhydrocarbyloxides, e.g.,

Si(OR) ZCOOR, Si(OR) (ZCOOR") and SiOR(ZCOOR) 3 of the recurring structural units are units of the formula,

wherein -G- represents a divalent organic radical containing from 2 to about 18 carbon atoms and attached to the adjacent oxygen atoms by saturated carbon atoms. Preferably, the radical G- contains from 2 to about carbon atoms. The terephthalate radical may be the sole dicarboxylate constituent of the recurring structural units, or up to about 25% of the recurring structural units may contain other dicarboxylate radicals, such as the adipate, sebacate, isophthalate, bibenzoate, hexahydroterephtha-late, diphenoxyethane 4,4 dicarboxylate, p,p-carbonyldibenzoate, and p,p'-sulfonyldibenzoate radicals.

The glycol, G(OH) from which the polyester is prepared may be any suitable dihydroxy compound containing from 2 to 18 carbon atoms, preferably from 2 to 10 carbon atoms, in which the hydroxyl groups are attached to saturated carbon atoms. Thus, may be of-the form p+1 2p+2 q-1) where p and q are positive integers and Y is a cycloaliphatic group, an aromatic group, an oxy group, or an arylenedioxy group. Examples of suitable glycols where q=1 include the polymethylene glycols, such as ethylene glycol, tetramethylene glycol, hexamethylene glycol, and decamethylene glycol as well as the branched chain glycols such as 2,2-dimethyl-1,3-propanediol and 2,2-dimethyl-l,4-butanediol.

Suitable glycols in which q=2 include cisor trans-pahexahydroxylylene glycol, bis-p-(Z-hydroxyethyl) benzene,

diethylene glycol,

bis- (4-hydroxybutyl) ether,

bis-p- B-hydroxyethoxy benzene, bis-1,4-(fi-hydroxyethoxy) -2,5-dichlorobenzene, bis-4,4'- ,B-hydroxyethoxy) diphenyl, 2,6-di(fi-hydroxyethoxymaphthalene,

bis- [p- (B-hydroxyethoxy phenyl] ketone,

bis- [p-( fl-hydroxyethoxy) phenyl] sulfone, and bis- [p-,/3-hydroxyetl1oxy) phenyl] difluoromethane.

Glycols in which q=3 include 4,4-bis(B-hydroxyethyl)biphenyl, 4,4-bis(,B-hydroxyethyl)dodecahydrobiphenyl, triethylene glycol, and

2,2-(ethylenedioxy bis-[p-phenyleneoxyl] )diethanol.

In general, the glycols in which q is greater than 3 are of lesser interest, although certain glycols such as tetraethylene glycol may be used. Mixtures of the glycols may be used. If desired, small amounts e.g., up to about weight percent, of a higher glycol such as a polyethylene glycol of high molecular weight may be added.

If desired, up to about 25% of a monohydroxymono the radical -G- 8 carboxy compound may be added to the glycol terephthalate to form a copolyester. For example, methyl 4-(Z-hydroxyethoxy)benzoate or its reaction product with ethylene glycol,

In determining the amount of oxysilicon compound added, the basis employed is the number of mols of the glycol component in the final polyester or copolyester. The total includes both the glycol in the form of glycol terephthalate and the glycol reacted with any other acid radicals present, calculated as the amount present at the conclusion of polymerization.

The preparation of a glycol ester of terephthalic acid, or a mixture of terephthalic acid with one or more other dicarboxylic acids, may be accomplished in any one of several ways. The glycol may be reacted with the free acid or acids, preferably at temperatures in a range 220- 280 C. at superatmospheric pressure. In place of the acid or acids, ester-forming derivatives may be used, i.e., derivatives which readily undergo polyesterification with a glycol or derivative thereof. For example, the acid chloride or a lower alkyl ester, such as the dimethyl ester, may be used. Formation of the glycol ester from the dimethyl ester mad the glycol can be facilitated by use of a conventional ester interchange catalyst such as manganous acetate, calcium acetate, or lanthanum acetate. Similarly, anester-forming derivative of the glycol may be used in place of the glycol; i.e., a derivative of the glycol which readily undergoes polyesterification with dicarboxylic acids or derivatives thereof. For example,'a cyclic oxidefrom which the corresponding glycol can be derived by hydrolysis may be used.

In order to carry out the polycondensation reaction rapidly and produce polymer of good quantity, use of an efficient polycondensation catalyst is essential. In accordance with the present invention, a condensation catalyst selected from the group consisting of glycol-soluble compounds of antimony and titanium is employed in the melt polymerization step. Examples of such catalysts include antimony trioxide, antimony pentoxide, antimony acetate, antimony trifluoride, antimony triglycolate, triphenyl antimony, tributyl antimony, tetraisopropyl titanate, tetraethyl titanate, tetrabutyl titanate, titanium tetrafluoride, sodium hydrogen hexabutyl titanate, and lanthanum titanate. By using thesecondensation catalysts, glycol esters of terephthalic acid can be polymerized rapidly to any desired relative viscosity value within the required range of 10 to about 17 to produce polymer of good quality as measured by a low concentration of free carboxyl groups or other polymer quality parameters. Various other materials, such as delusterants, color inhibitors, and the like may be added to the polymerization mixture if desired.

The invention will be further illustratedvby the following examples, which, however, are not intended to be.

limitative. The term relative viscosity refers to the ratio of the viscosity of a 10% solutionof the glycol terephthalate polyester in a mixture of 10 parts of phenol and 7 parts of 2,4,6-trichlorophenol by weight to the viscosity of the phenol-trichlorophenol mixture per se, measured in the same units at 25 C. The term melt viscosity refers to the absolute value of the viscosity, expressed in poises, of the polymer at the given temperature. The number of gram atoms of silicon in the added oxysilicon compound per gram mols of the glycol component in the polyester, as calculated herein, is equal numerically to mol percentage calculated on the basis of atoms of silicon per glycol radical in the final polyester. For brevity, the values given in the examples are reported as mol percent. Unless otherwise stated, anhydrous conditions are maintained until after the oxysilicon-modified polyester has been melt-spun, the fibers are spun in conventional manner into air of normal humidity, and are exposed to the moisture in the air after spinning.

Z-hydroxyethyl 4-(2-hydroxyethoxy) benzoate, may be employed.

9 EXAMPLE 1 In a series of experiments for which the results are recorded in Table I, a series of samples of polyethylene terephthalate containing various concentrations of silicon are prepared, together with a control sample containing no silicon. In each run 4536 parts of dimethyl terephthalate, 3062 parts of ethylene glycol, 2.04 parts of manganous acetate -4H O, and 1.36 parts of antimony trioxide are heated with evolution of methanol until no more methanol is evolved, the final temperature being about 230 C. The reaction mixture is then placed in an autoclave together with 1.5 parts of phosphoric acid, 13.6 parts of titanium dioxide, and the amount of tetraethyl orthosilicate indicated in the table. The temperature is increased to 275 C. and the pressure reduced to 1 mm. of mercury while the mixture is being agitated by a stirrer operated by means of air pressure which,

after one hour, is held constant at 60 psi The mixture is held at this constant pressure and temperature for a period of approximately 2 to 5 hours while glycol vapor is removed continuously and the mixture becomes more viscous. The rate of rotation of the stirrer decreases as the viscosity of the mixture increases; and when the stirrer speed reaches a value previously calibrated as equivalent to a reaction mass melt viscosity of approximately 2200 poises, the polymer is passed directly to a spinning chamber where it is extruded at 285 C. through a spinneret containing 34 holes, each 0.009 inch in diameter. The spun yarn has a denier of 340. The results obtained by determining the relative viscosity of the spun filaments as indicated in the table. The spun yard is drawn 3.8X over a curved hot plate at 97 C., the windup speed being 750 y.p.m. The properties of the yarn are given in the table.

TABLE I Preparation of polyethylene terephthalate at constant melt viscosity (2200 poises at 275 C.)

Quantity or Tetraethyl Orthosilicate Yarn Properties Add (1 Rel. Tenacity, Parts Mol Vise. g.p.d.

Percent Yield Point, g.p.d.

tion, Percent None 12.2 24.4 36. 6

The yarns produced in the first two batches recorded in Table I are cut to 15-inch lengths and processed to fabrics, both as 100% polyethylene terephthalate fabrics and the blends of 65% polyethylene terephthalate fibers with 35% cotton. After conventional finishing treatments the fabrics prepared from the extruded yarns containing 0.25 mol percent silicon are found to be relatively free from pills after normal use in garmets. Fabrics prepared in the same way from the extruded control yarn containing no silicon are found to be generally similar in appearance; however, the control fabrics exhibit severe pilling after a short period of use in garments under normal conditions.

Part of the polymer prepared in each of the first three batches recorded in Table I is extruded into containers, after which the containers are immediately closed and blanketed with dry nitrogen while the polymer samples solidify. After standing overnight with careful exclusion of water or water vapor from the polymer samples, they are remelted and spun into filaments. The melt viscosities of the silicon-containing polymers are approximately equivalent to the melt viscosity of the unmodified polyethylene terephthalate, while relative viscosity values approximately corresponding to those listed in the table are again obtained.

Another part of the polymer prepared in each of the first three batches recorded in Table I is extruded from the autoclave in a ribbon, quenched in water, and cut to flake. When samples of the flake are melted and extruded from a standard orifice in a melt index apparatus at 275 C., the silicon-containing polymers are found to have much lower melt viscosity than the unmodified polyethylene terephthalate. The calculated values for polyethylene terephthalate containing no silicon, 0.25 mol percent silicon, and 0.5 mol percent silicon are 1000, 240, and poises, respectively.

A second polymerization run using 0.25 mol percent tetraethyl silicate is carried out, except that polycondensation is continued until the stirrer speed reaches a value previously calibrated as equivalent to a reaction mass melt viscosity of approximately 5500 poises. Filaments extruded from the polymer are found to have a relative viscosity of 16, While filaments extruded from unmodi fied polyethylene terephthalate are found to have a relative viscosity of 30. EXAMPLE 2 A modified copolyester containing 0.25 mol percent silicon is prepared in accordance with the procedure of Example 1, using tetraethyl orthosilicate, except that the 4536 parts of dimethyl terephthalate is replaced by a mixture of 4445 parts of dimethyl terephthalate and 137 parts of sodium 3,5-di(carbometh0xy)benzenesulfonate. When the stirrer speed reaches a value previously calibrated as equivalent to a reaction mass melt viscosity of approximately 3500 poises, the polymer is passed directly to a spinning chamber Where it is extruded into filaments. The filaments are found to have a relative viscosity of 11.

A batch of polyethylene terephthalate/S-(sodium sulfo)isophthalate prepared in the same manner, except that no tetraethyl orthosilicate is added, is similarly extruded into filaments when the reaction mass melt viscosity reaches 3500 poises. The filaments are found to have a relative viscosity of 20.

In a similar experiment the procedure of Example 1 is followed, using 0.25 mol-percent tetraethyl orthosilicate, except that the 3062 parts of ethylene glycol is replaced by 6580 parts of trans-p-hexahydroxylylene glycol. Filaments of the silicon-containing polymer have a relative viscosity of 13. When a batch of poly(trans-phexahydroxylylene terephthalate) containing no silicon is extruded at the same melt viscosity, the filaments are found to have a relative viscosity of 19.

EXAMPLE 3 Polymer preparation as described in Example 1 is repeated, except that in place of tetraethyl silicate other silicon-containing materials are used, as listed in Table II. In each case the number of parts of the siliconcontaining material is indicated in the table, together with the mol percentage level of silicon which this quantity represents. When the stirrer speed reaches a value previously calibrated as equivalent to a reaction mass melt viscosity of approximately 2200 poises, the reaction is terminated. Relative viscosity values for samples of each of the polymers is obtained, as indicated in the table.

The sample of water glass employed in this example comprises a 40% solution of Na O-(SiO in water. The material is introduced into the autoclave in a dispersion .in ethylene glycol, prepared by placing 500 parts of the glycol in a Waring Blendor and adding the water glass to the stirred glycol in small increments. The sample of ethyl polysilicate employed in this example has the empirical composition, I

OEt

EtO (-Si-0) but.

OEt

TABLE II 11 Preparation of polyethylene terephthalate modified with various silicon-containing materials at constant melt viscosity (2200 poises at 275 C.)

No. of M01 Rel. Silicon-Containing Material Parts Percent Visc. i Added Polymer (1) None 0 22 (2) Tetrabutyl orthosilicate 18. 6 0. 25 13.9 (3) Tetra-(2-hydroxyethyl) orthosilicate 15.8 0. 25 15.2 (4) Water Glass 60.0 3.25 9.3 (5) fl-carbethoxypropyltriethoxysilane. 23. 2 0.375 15.2 (6) B-carbethoxypropylmethyldi- 32. 6 0.50 16.3

ethoxysilane. (7) Ethyl polysilieate 17.5 0.50 12.2 (8) Ethyl polysilicate 8. 7 0.25 14. 6 (9) Diphenyl diethoxysilane 31. 9 0. 50 13.8 (10) Methyl triethoxysilana 15.6 0.375 14.1 (11) Hexaethoxydisiloxane 13.6 0.32 15.5 (12) B-carbethoxyethyldimethyl 24. 0 0.50 ea. 15

ethoxysilane.

Based on solids content.

EXAMPLE 4 In each of a series of runs, 4536 parts of dimethyl terephthalate, 3062 parts of ethylene glycol, 2.04 parts of manganous acetate 4H O, and 1.36 partsv of antimony trioxide are heated with evolution of methanol until no more methanol is evolved, the final temperature being about 230 C. The reaction mixture is then placed in an autoclave together with 1.5 parts of phosphoric acid and 13.6 parts of titanium dioxide. The temperature is increased to 275 C. and the pressure reduced to 1 mm. of mercury while the mixture is being agitated by a stirrer operated by means of air pressure which, after one hour, is held constant at p.s.i.'While the mixturei 5 held at constant temperature and pressure, glycol vapor is removed continuously and the mixture becomes more viscous. The rate of rotation of the stirrer decreases as the viscosity of the mixture increases, and when the stirrer speed reaches a fixed predetermined value corresponding to about 1500 poises, the reaction is stopped by introducing dry nitrogen to bring the vessel to atmospheric pressure.

To the first autoclave is then added 6.8 parts (0.16 mol percent) hexaethoxydisiloxane, while 13.6 parts (0.32 mol percent) hexaethoxydisiloxane is added to the second autoclave. No additive is introduced in the third autoclave. After five minutes at atmospheric pressure, the melt viscosity in each autoclave remains at approximately the same value previously observed, 1500 poises. The polymer is then passed from each autoclave directly to a spinning chamber where it is extruded at 285 C. through a spinneret containing 34 holes, each 0.009 inch in diameter. The spun yarn from the first autoclave has a relative viscosity of 18.8, while the yarn from the second autoclave has a relative viscosity of 14.7 and the yarn from the third autoclave a relative viscosity of 21.1.

Samples of the yarns, after standing in air, are remelted and extruded from a standard orifice in a melt index apparatus at 275 C. The silicon-containing polymers from the first and second autoclave have calculated melt viscosity values of only 840 and 400 poises, respectively, as contrasted with 1380 poises for the unmodified polyethylene terephthalate from the first autoclave.

EXAMPLE 5 Polyethylene terephthalate containing no silicon additive is prepared in accordance with the general procedure of Example 4, except that the polycondensation is stopped when the melt viscosity reaches 500 poises. The polymer is extruded from the autoclave in a ribbon, quenched in water, and cut into flake; after which the flake is thoroughly dried, using recirculating warm, dry air. The relative viscosity of the polymer is 15.

Quantities of an estersil comprising a solid supercol- Wt. Approx., Melt Additive percent M01 Rel. Vise. Vise.

percent (poises) (1) None (control) 14.1 463 (2) Estersil (insoluble) 1 1.5 13.8 490 (3) Estersil (insoluble) 2.5 3.75 14.5 520 a (4) Estersil (insoluble) 5 7.5 14.5 510 (5) Hexaethoxydisiloxane (soluble 0. 9 1 12. 8 3, 000

As shown by the data 1n the table, addition of estersils loidal aggregate of silica'of fine particle size (less than 20 millimicrons) surface esterified with butanol as disclosed by Iler in his US. Patent No. 2,857,355 is mixed thoroughly ,with samples of the polyethylene terephthalate flake in the concentrations indicated in Table III below. The samples are melted and extruded from a standard orifice in a melt index apparatus at 275 C. As a control, a sample of unmodified polymer is extruded in the same Way. Hexaethoxydisiloxane in the indicated amount is absorbed into an additional sample of the flake and this sample also is melted and extruded. The melt viscosity and final relative viscosity of each of the polymer samples is given in the table.

TABLE III Melt viscosity vs. relative viscosity for samplels of polyethylene terephthalate of 15 relative viscosity mixed with soluble and insoluble silicon additives to finished polymer produces little if any change in the,

melt viscosity-relative viscosity relationship, while the use of soluble silicon additives in accordance with the invention produces a marked effect even with finished polymer.

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to 'be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

We claim:

1. An improvement in the process of melt spinning a glycol terephthalate polyester to produce textile fibers of sufliciently low molecular weight to substantially decrease pilling in fabrics containing the fibers, which process includes melt-polymerization of an ester of terephthalic acid and a glycol of 2 to 18 carbon atoms free from aliphatic unsaturation, in the presence of a condensation catalyst, to a final temperature of about 250 to about 300 C. and a final pressure of less than 10 mm. of mercury to form an anhydrous melt; wherein the.improvernent comprisesvconducting said melt-polymerization in the presence of a condensation catalyst selected from the group consisting of glycol-soluble compounds of antimony or titanium and adding an oxysilicon compound prior to melt spinning to'form an anhydrous melt having a melt viscosity at 275 C. of about 1000 to about 6000 poises; said oxysilicon compound being added in the proportion of about 0.1 to 0.75 gram atom of silicon in the added compound per gram mols of said glycol component in the polyester and being selected from the group consisting of wherein R, R' and R" are selected from the group consisting of hydrocarbyl and oxyhydrocarbyl radicals of 1 to 6 carbon atoms, Z is a divalent saturated hydrocarbon group of 1 to 6 carbon atoms, x is a number from 1 to 20, and n is a number from 0 to 2; maintaining said poly- 13 ester anhydrous and melt-spinning it to form fibers; and finally exposing the spun fibers to moisture.

2. The process as defined in claim 1 wherein said oxysilicon compound is tetraethyl orthosilicate.

3. The process as defined in claim 1 wherein said oxysilicon compound is added in the proportion of 0.25 to 0.75 gram atom of silicon per 100 gram mols of glycol component in the polyester.

14 References Cited FOREIGN PATENTS 5/1958 Great Britain. 5/1963 Japan.

J. H. WOO, Assistant Examiner. 

1. AN IMPROVEMENT IN THE PROCESS OF MELT SPINNING A GLYCOL TEREPHTHALATE POLYESTER TO PRODUCE TEXTILE FIBERS OF SUFFICIENTLY LOW MOLECULAR WEIGHT TO SUBSTANTIALLY DECREASE PILLING IN FABRICS CONTAINING THE FIBERS, WHICH PROCESS INCLUDES, MELT-POLYMERIZATION OF AN ESTER OF TEREPTHITHALIC ACID AND A GLYCOL OF 2 TO 18 CARBON ATOMS FREE FROM ALIPHATIC UNSATURATION, IN THE PRESENCE OF A CONDENSATION CATALYST, TO A FINAL TEMPERATURE OF ABOUT 250* TO ABOUT 300*C. AND A FINAL PRESSURE OF LESS THAN 10 MM. OF MERCURY TO FORM AN ANHYDROUS MELT; WHEREIN THE IMPROVEMENT COMPRISES CONDUCTING SAID MELT-POLYMERIZATION IN THE PRESENCE OF A CONDENSATION CATALYST SELECTED FROM THE GROUP CONSISTING OF GLYCOL-SOLUBLE COMPOUNDS OF ANTIMONY OR TITANIUM AND ADDING AN OXYSILICON COMPOUND PRIOR TO MELT SPINNING TO FORM AN ANHYDROUS MELT HAVING A MELT VISCOSITY AT 275*C. OF ABOUT 1000 TO ABOUT 6000 POISES; SAID OXYSILICON COMPOUND BEING ADDED IN THE PROPORTION OF ABOUT 0.1 TO 0.75 GRAM ATOM OF SILICON IN THE ADDED COMPOUND PER 100 GRAM MOLS OF SAID GLYCOL COMPONENT IN THE POLYESTER AND BEING SELECTED FROM THE GROUP CONSISTING OF. 